Abstract
We have designed and tested several synthesis routes targeting a highly fluorinated disordered rocksalt (DRX) cathode, Li1.2Mn0.4Ti0.4O1.6F0.4, with each route rationalized by thermochemical analysis. Precursor combinations were screened to raise the F chemical potential and avoid the formation of LiF, which inhibits fluorination of the targeted DRX phase. MnF2 was used as a reactive source of F, and Li6MnO4, LiMnO2, and Li2Mn0.33Ti0.66O3 were tested as alternative Li sources. Each synthesis procedure was monitored using a multi-modal suite of characterization techniques including X-ray diffraction, nuclear magnetic resonance, thermogravimetric analysis, and differential scanning calorimetry. From the resulting data, we advance the understanding of oxyfluoride synthesis by outlining the key factors limiting F solubility. At low temperatures, MnF2 consistently reacts with the Li source to form LiF as an intermediate phase, thereby trapping F in strong Li-F bonds. LiF can react with Li2TiO3 to form a highly lithiated and fluorinated DRX (Li3TiO3F); however, MnO is not easily incorporated into this DRX phase. Although higher temperatures typically increase solubility, the volatility of LiF above its melting point (848 °C) inhibits fluorination of the DRX phase. Based on these findings, metastable synthesis techniques are suggested for future work on DRX fluorination.
| Original language | English |
|---|---|
| Pages (from-to) | 7015-7028 |
| Number of pages | 14 |
| Journal | Chemistry of Materials |
| Volume | 34 |
| Issue number | 15 |
| DOIs | |
| State | Published - Aug 9 2022 |
Funding
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office, under the Applied Battery Materials Program, of the U.S. Department of Energy (DOE) under contract no. DE-AC02-05CH11231, and by Umicore Specialty Oxides and Chemicals. We also acknowledge support from the National Science Foundation Graduate Research Fellowship under grant #1752814. The NMR results reported here made use of shared facilities of the UCSB MRSEC (NSF DMR #1720256), a member of the Materials Research Facilities Network ( www.mfn.org ). X-ray data measurement and part of XRD data analysis were conducted at the Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility. Synchrotron X-ray experiments by J.B. and F.W. were supported by the U.S. DOE Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office. The use of NSLS-II at Brookhaven National Laboratory was supported by the U.S. DOE, Office of Basic Energy Sciences under contract no. DE-SC0012704.